In acoustic (e.g., ultrasound) imaging, or other active acoustics imaging, an array of transducers first transmits a pulse into the medium, usually with appropriate delay to generate a focused beam, and then receives the echo. Beamforming is used to reconstruct an image of the medium. The quality of the image is related to the point-spread function (PSF), or response of the imaging system to a single point. The PSF is related to the aperture of the array. In the far field approximation, the lateral profile of the PSF is the square of the Fourier transform of the aperture amplitude distribution. If no apodization is used it would be a sinc2 function.
However part of the aperture may be blocked by one or several obstacles. In medical ultrasound, the obstacle could be a rib. For example, ultrasound imaging of the heart through the chest (transthoracic ultrasound imaging) is complicated by the presence of ribs which may block part of the aperture if it is too large. If the blocked part of the aperture is along the edge of the aperture, this will result in a loss of resolution. If it is within the aperture, it will result in grating lobes that may severely reduce the image quality. The same phenomenon results from a gap in the aperture, which can be caused by non-functioning transducer array elements, or if one attempts to image coherently with two ultrasound arrays that are separated by a gap. On the other hand, if a smaller aperture is employed which fits in the space between two ribs (hereafter referred to as an “intercostal gap”), then the field of view and resolution of the ultrasound image is limited.
Accordingly, it would be desirable to provide a method and system for ultrasound imaging which can use a larger coherent aperture across several intercostal spaces.
In one aspect of the invention, a method comprises: employing an acoustic transducer array to produce image data for the imaging region, wherein there are one or more obstructions between the acoustic transducer array and at least a portion of the imaging region; exploiting redundancy in transmit/receive pair paths among the acoustic transducers in the acoustic transducer array to compensate for missing image data of the imaging region due to the one or more obstructions; and producing an image of the imaging region from the compensated image.
In some embodiments, exploiting redundancy in transmit/receive pair paths among the acoustic transducers in the acoustic transducer array to compensate for missing image data of the imaging region due to the one or more obstructions and producing an image of the imaging region from the compensated image data comprises: determining an inverse filter for the acoustic transducer array, wherein when the inverse filter is multiplied by an angular spectrum for the acoustic transducer array with respect to the imaging region in the presence of the one or more obstructions, it produces an ideal angular spectrum for the acoustic transducer array with respect to the imaging region which would exist in the absence of the one or more obstructions; weighting a signal produced by each transmit/receive pair of elements in the acoustic transducer array by a value of the inverse filter corresponding to the angular frequency of the transmit/receive pair, and generating an acoustic image by summing the weighted signals of all the transmit receive pairs.
In some embodiments, exploiting redundancy in transmit/receive pair paths among the acoustic transducers in the acoustic transducer array to compensate for missing image data of the imaging region due to the one or more obstructions and producing an image of the imaging region from the compensated image data comprises: performing at least first and second transmit-and-receive operations using at least first and second apodization functions, including: performing the first transmit-and-receive operation by employing the acoustic transducer array to transmit a first acoustic wave to the imaging region and to receive back from the imaging region a first acoustic echo and to produce therefrom first image data, wherein the first apodization function is applied to the acoustic transducer array to produce a first transmit aperture and a first receive aperture for the first transmit-and-receive operation, and performing the second transmit-and-receive operation by employing the acoustic transducer array to transmit a second acoustic wave to the imaging region and to receive back from the imaging region a second acoustic echo and to produce therefrom second image data, wherein the second apodization function is applied to the acoustic transducer array to produce a second transmit aperture and a second receive aperture for the second transmit-and-receive operation; and producing an image of the imaging region by combining the first image data with the second image data. The at least first and second apodization functions are determined from an inverse filter for the acoustic transducer array with respect to the imaging region, wherein when the inverse filter is multiplied by an angular spectrum for the acoustic transducer array with respect to the imaging region in the presence of the one or more obstructions, it produces an ideal angular spectrum for the acoustic transducer array with respect to the imaging region which would exist in the absence of the one or more obstructions.
In some embodiments, exploiting redundancy in transmit/receive pair paths among the acoustic transducers in the acoustic transducer array to compensate for missing image data of the imaging region due to the one or more obstructions and producing an image of the imaging region from the compensated image data comprises performing an RF data (pre-detection) based or image based deconvolution algorithm.
In another aspect of the invention, an apparatus for imaging an imaging region, comprises: an acoustic transducer array configured to produce image data for the imaging region, wherein there are one or more obstructions between the acoustic transducer array and at least a portion of the imaging region; and one or more processors, configured to exploit redundancy in transmit/receive pair paths among the acoustic transducers in the acoustic transducer array to compensate for missing image data of the imaging region due to the one or more obstructions, and to produce an image of the imaging region from the compensated image data.
In some embodiments, the one or more processors are configured to exploit redundancy in transmit/receive pair paths among the acoustic transducers in the acoustic transducer array to compensate for missing image data of the imaging region due to the one or more obstructions, and to produce an image of the imaging region from the compensated image data, by: determining an inverse filter for the acoustic transducer array, wherein when the inverse filter is multiplied by an angular spectrum for the acoustic transducer array with respect to the imaging region in the presence of the one or more obstructions, it produces an ideal angular spectrum for the acoustic transducer array with respect to the imaging region which would exist in the absence of the one or more obstructions; weighting a signal produced by each transmit/receive pair of elements in the acoustic transducer array by a value of the inverse filter corresponding to the angular frequency of the transmit/receive pair, and generating an acoustic image by summing the weighted signals of all the transmit receive pairs.
In some embodiments, the one or more processors are configured to exploit redundancy in transmit/receive pair paths among the acoustic transducers in the acoustic transducer array to compensate for missing image data of the imaging region due to the one or more obstructions, and produce an image of the imaging region from the compensated image data, by: performing at least first and second transmit-and-receive operations using at least first and second apodization functions, including: performing the first transmit-and-receive operation by employing the acoustic transducer array to transmit a first acoustic wave to the imaging region and to receive back from the imaging region a first acoustic echo and to produce therefrom first image data, wherein the first apodization function is applied to the acoustic transducer array to produce a first transmit aperture and a first receive aperture for the first transmit-and-receive operation, and performing the second transmit-and-receive operation by employing the acoustic transducer array to transmit a second acoustic wave to the imaging region and to receive back from the imaging region a second acoustic echo and to produce therefrom second image data, wherein the second apodization function is applied to the acoustic transducer array to produce a second transmit aperture and a second receive aperture for the second transmit-and-receive operation; and producing an image of the imaging region by combining the first image data with the second image data. The at least first and second apodization functions are determined from an inverse filter for the acoustic transducer array with respect to the imaging region, wherein when the inverse filter is multiplied by an angular spectrum for the acoustic transducer array with respect to the imaging region in the presence of the one or more obstructions, it produces an ideal angular spectrum for the acoustic transducer array with respect to the imaging region which would exist in the absence of the one or more obstructions.
In some embodiments, the one or more processors are configured to exploit redundancy in transmit/receive pair paths among the acoustic transducers in the acoustic transducer array to compensate for missing image data of the imaging region due to the one or more obstructions and producing an image of the imaging region from the compensated image data by performing an RF data (pre-detection) based or image based deconvolution algorithm.